Ritonavir, a potent inhibitor of cytochrome P450 3A4 (CYP3A4) and CYP2D6, can cause clinically significant increases in serum levels of other protease inhibitors (PIs). Pharmacokinetic enhancement of certain PIs with low-dose ritonavir can increase drug concentrations of these PIs while allowing a reduction in pill burden, dosing frequency, and food restrictions.

The following table shows evidence-based possibilities for adult dosages of ritonavir-boosted PIs. Not all are approved by the U.S. Food and Drug Administration.

For more information, see the Database of Antiretroviral Drug Interactions.

Protease Inhibitor Adult Dosing Options Amprenavir As of June 2005, no longer manufactured for adult dosing; consider fosamprenavir. Atazanavir Atazanavir 300 mg QD + ritonavir 100 mg QD Darunavir Darunavir 600 mg BID + ritonavir 100 mg BID Fosamprenavir Fosamprenavir 700 mg BID + ritonavir 100 mg BID* Fosamprenavir 1,400 mg QD + ritonavir 200 mg QD* # Fosamprenavir 1,400 mg QD + ritonavir 100 mg QD* # Indinavir Indinavir 800 mg BID + ritonavir 100 mg BID* Indinavir 800 mg BID + ritonavir 200 mg BID* Indinavir 400 mg BID + ritonavir 400 mg BID* Lopinavir Lopinavir 400 mg + ritonavir 100 mg BID (coformulated as Kaletra)* Lopinavir 800 mg + ritonavir 200 mg QD (coformulated as Kaletra)# § Saquinavir Saquinavir 1,000 mg BID + ritonavir 100 mg BID Saquinavir 1,600 mg QD + ritonavir 100 mg QD Saquinavir 400 mg BID + ritonavir 400 mg BID Tipranavir Tipranavir 500 mg BID + ritonavir 200 mg BID

Abbreviations: BID = 2 times per day; QD = once daily * When used in combination with efavirenz or nevirapine, may require dosage adjustment. See Dosage Adjustments for ARV-ARV Drug Interactions. # Once-daily dosing of fosamprenavir or lopinavir is not recommended for PI-experienced patients. § Once-daily lopinavir/ritonavir should not be used in combination with efavirenz, nevirapine, amprenavir, fosamprenavir, or nelfinavir (dosage adjustment not established).